1. Field of the Invention
The present invention relates to an organic electroluminescent device of the active matrix (AM) and passive matrix (PM) types, and a method for manufacturing the same. Particularly, the present invention relates to an organic electroluminescent device and a manufacturing method therefore, having a structure that can prevent damage of walls and organic material layers caused by deformation of a metal mask used during a manufacturing process to deposit organic material layers.
2. Description of the Related Art
Organic electroluminescence is a phenomenon wherein excitons are formed in an organic (low molecular or high molecular) material thin film by re-combining holes injected through an anode with electrons injected through a cathode, and a light of specific wavelength is generated by energy from thus formed excitons. The basic structure of an organic electroluminescent device using the phenomenon and a method for manufacturing the same will be described hereinafter.
FIG. 1 is a plane view of an organic electroluminescent device, in accordance with the present invention, and FIG. 2 is a cross-sectional view of the organic electroluminescent device of FIG. 1, as taken along line A-A. Certain portions of the organic electroluminescent device of FIG. 1 are basic structures, in accordance with the related art. Those basic structures will now be described in the following paragraphs.
The basic structure of an organic electroluminescent device includes a glass substrate 1, an anode electrode layer 2 formed on the upper side of the glass substrate 1, an organic material layer 3 (hereinafter, referred to as “organic EL layer”) formed on the anode electrode layer 2, and a cathode electrode layer 4 formed on the organic EL layer 3.
The organic EL layer 3 has a structure wherein a hole transport layer, a light emitting layer and an electron transport layer are stacked in order. Each cathode electrode layer 4 maintains a certain space from adjacent cathode electrode layers 4. The anode electrode layer 2 acts as an anode electrode, and the cathode electrode layer 4 acts as a cathode electrode.
A wall 5 separates two adjacent cathode electrode layers 4. The wall 5 is formed in an area between two adjacent cathode electrode layers 4. The wall 5 is separated from the anode electrode layer 2 by an insulating layer 4a. Although organic material and cathode electrode material are deposited on the upper side or top of each wall 5 during the processes of forming the organic EL layer 3 and cathode electrode layer 4, neither functions as a component of the device.
The organic electroluminescent device having the above structure is manufactured by the following processes.
First, a plurality of anode electrode layers 2 are deposited on a glass substrate 1, and then an insulating layer 4a is formed on the entire surface area of the substrate 1 except predetermined areas (luminescent areas).
Then, a plurality of walls 5 crossing the anode electrode layers 2 are formed thereon, followed by forming organic EL layers 3 and cathode electrode layers 4 on the entire structure including the walls 5.
For the organic EL layers 3, different organic materials, corresponding to R (red), G (green) or B (blue), are deposited in each luminescent area. FIG. 2 shows that one organic EL layer 3 and one cathode electrode layer 4 are formed between two walls 5, but the same structure of one organic EL layer and metal layer is formed at both sides to form R, G and B luminescent areas.
A metal mask is used to form an organic EL layer corresponding to each pixel area, and the relation between the mask and walls 5 will be described with reference to FIG. 5 below.
FIG. 3 is a cross-sectional view of the organic electroluminescent device of FIG. 1 as taken along line B-B, which illustrates the state just before forming the organic EL layers 3 and after forming the walls 5.
As described above, a mask M is used to form the organic EL layers 3, and the mask M is positioned on the walls 5. A magnetic field or force of a magnet (not shown), installed under the substrate 1, acts on the mask M. Therefore, the process of forming the organic EL layers can stably proceed without any movement of the mask M.
During the deposition process of organic EL layers, the mask M is attracted toward the substrate 1 by the magnet's force acting on the mask M, and thus the mask M is brought into contact with the walls 5, as shown in FIG. 3B, especially at the edge portion of the walls 5. This physical contact between the mask M and the walls 5 causes the walls 5 to be damaged (especially at the edges of the walls 5), thereby generating particles of the walls 5.
For example, after an organic EL layer corresponding to R luminescent area is formed, another organic EL layer corresponding to an adjacent G luminescent area or B luminescent area is formed. During the process of forming an organic EL layer corresponding to the G luminescent area or the B luminescent area, the mask M may sag toward the substrate 1 due to the magnet's attraction force, as shown in FIG. 3B.
Therefore, the mask M is brought into physical contact with the organic EL layer 3 in the R luminescent area, thereby damaging the organic EL layer, in addition to generating organic particles from the walls 5.
If the organic particles from damaged walls 5 exist on the organic EL layer 3, the particles may cause leakage current in the device, leading to defects of the display.